Synthesis and circularly polarized luminescence properties of BINOL-derived bisbenzofuro[2,3-b:3’,2’-e]pyridines (BBZFPys)

Abstract

A series of optically active bisbenzofuro[2,3-b:3’,2’-e]pyridine (BBZFPy) derivatives was synthesized starting with the readily available (S)- and (R)-1,1’-bi-2-naphthols through a palladium-catalyzed multiple intramolecular C–H/C–H coupling as the key ring-closure step. The effect of terminal tert-butyl substituents on the BBZFPy skeleton was systematically investigated to uncover a unique aggregation-induced enhancement of CPL characteristics in the solid state. The crystal structures of the coupling products were also evaluated by single crystal X-ray analysis and the well-ordered intermolecular stacking arrangements appeared to be responsible for the enhanced CPL.

Palladium-catalyzed cross-dehydrogenative coupling of (hetero)arenes

“…In 2020, the same experimental conditions were successfully applied to the intramolecular CDC of 2,6-diaryloxypyridines obtained from axially chiral 1,1′-bi-2-naphthol: in this case, the reactions produced a series of optically active bisbenzofuro[2,3- b :3′,2′- e ]pyridines, which were then subjected to spectroscopic characterization via circularly polarized luminescence (CPL) spectroscopy in solution and thin films. 218…”

“…In 2020, the same experimental conditions were successfully applied to the intramolecular CDC of 2,6-diaryloxypyridines obtained from axially chiral 1,1′-bi-2-naphthol: in this case, the reactions produced a series of optically active bisbenzofuro[2,3-b:3′,2′-e]pyridines, which were then subjected to spectroscopic characterization via circularly polarized luminescence (CPL) spectroscopy in solution and thin films. 218 A very few examples of Pd-catalyzed intramolecular CDC reactions between two different heteroarenes for the synthesis of pentacyclic compounds have also been reported. In 2001, in a more extended work dedicated to the preparation of indolocarbazoles via different photochemical and thermal reactions, Merlic and co-workers also reported one example of a Pd-catalyzed intramolecular CDC reaction of 1,1′-carbonyldi-1Hindole: C-H bonds at the C2 position of both indole rings were coupled to give the corresponding 6H-imidazo[1,5-a:3,4-a′] diindol-6-one.…”

Synthesis and Optical Properties of Axially Chiral Bibenzo[b]carbazole Derivatives

“…8 Upon this concept, we previously achieved the synthesis of chiral bisbenzofuro[2,3-b:3′,2′-e]pyridine (BBZFPy) derivatives uti-lizing the palladium-catalyzed C−H/C−H oxidative coupling reaction, 9 embedding the hydroxy groups of 1,1′-bi-2-naphtol (BINOL) into the polyaromatic scaffolds (Scheme 1a). 10 These compounds exhibited CPL characteristics, and unique aggregation-induced improvement of the g lum value up to 6.68 × 10 −3 was observed. Meanwhile, a limited number of CPL active compounds have been developed on the basis of 1,1′-bi-2-naphthylamine (BINAM), 11 an amine analogue of BINOL.…”

“…On the other hand, axially chiral CPL active molecules with π-extended poly­(hetero)­aromatic skeletons have been scarce probably because of the synthetic difficulty in obtaining them as pure enantiomers . Upon this concept, we previously achieved the synthesis of chiral bisbenzofuro­[2,3- b :3′,2′- e ]­pyridine (BBZFPy) derivatives utilizing the palladium-catalyzed C–H/C–H oxidative coupling reaction, embedding the hydroxy groups of 1,1′-bi-2-naphtol (BINOL) into the polyaromatic scaffolds (Scheme a) . These compounds exhibited CPL characteristics, and unique aggregation-induced improvement of the g lum value up to 6.68 × 10 –3 was observed.…”